What happens if multiple admins click to initiate a background reindex simultaneously?

Question

* Will the server allow multiple reindex jobs to run simultaneously?
* Will the server queue up multiple background reindex job requests so they run back to back?
* Will the server prevent multiple background reindex jobs from running simultaneously?
* Will the additional requests be ignored until another reindex is suggested and an Admin chooses to reindex?

I'm hoping it's #3 & #4.

Nic Brough -Adaptavist- · Accepted Answer

Once the first one is running, further requests are ignored until the first one has ended.

If you kick off a full re-index while a background one is running, then the background one is terminated. And you can't (easily or quickly) start a background one while a full one is running.